This study seeks to 1) explore the mechanism of action of vascular smooth muscle, 2) to characterize those changes in vascular smooth muscle function occurring in association with hypertension, and 3) to determine what role these changes play in the induction maintenance and sequelae of hypertension in rats. The first hypothesis is that the changes in excitability of isolated helical strips of artery from hypertensive rats is due to an altered binding of calcium by the muscle membrane. In a muscle bath we will measure the responses of arterial strips from DOCA-hypertensive and normal rats, and from rats with altered plasma calcium concentrations. Plasma calcium will be altered by parathyroidectomy and diet. We will also determine the effect of barium on isolated vascular smooth muscle. The second hypothesis is that decreased maximum contractility of arterial strips from hypertensive rats is due to an altered amount of collagen and elastin in the artery wall or an altered connection of the collagen and elastin with smooth muscle cells in the artery wall. The first possibility will be explored biochemically while the questions of connection will be explored via transmission electron microscopy.